Idle troubles

The Mini’s idle has always been a bit rough (lightweight flywheel, uprated cam, solid mount subframe) but lately it’s been worse than usual. Time to figure it out.

Long (looooong) story short, it was a combination of things:

-The new 123ignition electronic distributor does *not* like copper core ignition leads, even with suppressor spark plug caps. The interference causes about 10 degrees of spark scatter at idle. I’ve gone back to the old mechanical distributor with points until I get around to making some carbon-core suppressed leads.

-Rocker clearances. This one’s entirely my fault. I checked them as part of the 10,000km service and set them to the standard 12 thou, completely forgetting that Kent Cams recommends 17 thou for the MD266. 12 thou is too much overlap for a reasonable idle. Set them to 17 thou and magic happens! It’ll idle at 800 rpm!

-Carburettor balance: one of the carburettor’s idle screws was very loose and it would never settle into one place, meaning the idle balance was always a bit off. I tapped the idle screw holes larger and fitted bigger hex socket screws (for easier adjustment) and now the carbs stay in balance.

Things it was not:

-Mixture. I was seeing some wild numbers when the rocker clearances were too tight, but once I’d corrected them it idles at a super stable 14.5:1.

-Lightweight flywheel. I fitted a standard Morris 1300 flywheel, a 22kg hunk of pig iron with a ring gear on the outside. Made no difference to the smoothness, just slowed the engine down. I’d forgotten how difficult it is to swap a flywheel with the engine in place, but luckily I found my old bent 1/2″ ring spanner, the one I bent back in 1998 when working on the Mini van in the carpark.

With that sorted, I now return to adjusting the front alignment (over and over again) to dial out the weird twitchiness that started after I installed the Quaife ATB. The good folks over at mostly confirm what Quaife say: that during normal driving you shouldn’t know it’s there, apart from heavier steering.
We’ve confirmed that there *is* a break in period (despite what Quaife say) where the fresh new diff loosens up, and it is indeed behaving a little better, though there’s still a disturbing weave to one side or the other when balancing the accelerator between drive and coast. More fettling needed.

Lucas is a four letter word.

The rebuilt Lucas 16ACR alternator started to fail around 2017, so we splashed out and bought a brand new one, with a whopping 35A output.
And now, 4 years later, that one’s begun to fail too, with the warning light flickering like a candle.

I’m a little bit over this. Let’s go see what’s at the junk yard.

Would you look at that! Someone’s carelessly left a high performance lightweight Mini race alternator installed in a Daihatsu Charade. I’ll have that, thanks…

This tiny Denso alternator weighs half what a Lucas alternator weighs, yet puts out 40A. Very nice. Unfortunately it was also very tired and needed an overhaul, and when I priced up the rebuild parts it turned out to be cheaper to just buy a whole new one. So I did, and made up a new adjuster bracket.

The new alternator also makes 60A, and so far seems to work quite well.

If I were doing it again I’d just go for the Minispares competition alternator: the same lightweight alternator, but with all the required brackets for a drop-in replacement, and about the same cost as buying and modifying an alternator yourself.


I took the Mini to Beach Hop, a week of 1960’s Americana on the Coromandel. The Coromandel is pretty much all winding, hilly roads: perfect for a Mini (but not so great for the big yank tanks). I suspect I might have been a bit too enthusiastic with the cornering speeds, letting the inside wheel lift and spin a bit too often. The gearbox developed an unusual clunk when starting off, and the wheels had a bit more rotational play than seemed right, especially since I’d just rebuilt the gearbox and shimmed all the slop out.
Nothing for it but to pull the gearbox again and see what’s going on.

Oh my, look at all those pretty sparkles in bronze and hardened steel blue.

They’re what’s left of the diff’s planetary gear bushes:

Turns out a standard diff really isn’t up to an uprated engine and enthusiastic use. I guess I could install a cross-pin diff, but since this is the second time it’s been apart in as many months I went for the nuclear option:

Quaife Automatic Torque Biasing diff. It’s a geared diff (like a Torsen) so it never fully locks up, but it does direct the torque to the wheel with the most grip (up until one wheel lifts off, then it acts more like an open diff).
It’s also indestructible. Allegedly. We’ll see.
I slapped it in there, put everything back together, and went for a test drive: the damned thing tried to torque bias me into the next lane.

Once the panic had subsided (I spent *how much* just to ruin the Mini?) I did a bit more research and have made substantial improvements.

The main problem in my case was driveshaft-angle-induced torque steer. When a driveshaft acts through the CV joint at an angle most of the torque tries to rotate the wheel in the drive direction, but some of the torque tries to turn the steering knuckle. Our Mini was at a sensible, relatively tall ride height, which gave the driveshafts unequal angles due to the Mini’s unequal driveshaft lengths. This meant the left wheel got more steering torque than the right wheel, leading to a pull to the right when accelerating (and to the left when decelerating).

The cure was to spend a few days grovelling around under the Mini with a digital angle gauge, lowering the suspension until the driveshafts are perfectly perpendicular to the wheels. Driveshaft not acting on an angle = no torque trying to steer the wheels. The adjustments were surprisingly sensitive, with very small changes to ride height disturbing the driveshaft angles quite a lot. And every time I adjusted something I had to go for a drive to let the suspension settle… my neighbours probably think I’m a hoon (I mean, I *am*, but they don’t need to know that). In the end it only needed to drop about 12mm, so it’s ended up pretty much standard height.

That cured 95% of the scary torque steer. Making sure both sides had exactly the same camber and caster cured most of the rest, though the steering is still a bit lively when the diff’s hunting for traction while cornering or on a slippery surface (expected), and there’s a disturbing twitch when lifting off at 100kph.

Traction through corners is *ridiculous* now, as long as you’re ready to show the steering wheel who’s boss. It’s not arduous, you don’t need muscles like the hulk, but it’s a big change from the Mini’s previously light, precise, communicative steering.

I’m still not sure if I like it or not. I might get used to it. Or not; watch this space for a discount priced, lightly used, Quaife LSD.

123ignition distributor

The old Lucas 45D4 distributor was doing a good job from 2000rpm and up, but the timing was too advanced at idle, making starting difficult. It could be altered to make it better: build a distributor testing machine, dismantle the distributor, make new springs, change the advance weights, test and test and test again until it’s right… or I could buy a modern digital distributor.

123ignition make few drop-in replacements. The basic model has 14 pre-set advance curves to choose from, and once set is ready to go. Other models are programmable over USB or even Bluetooth. The programmable models sounded good, but 123ignition made it clear they would never release an API or even document the communication protocols, even if the company went under. I’m old enough to have owned devices which became paperweights when the app that ran them was no longer available, and I’d prefer not to risk that with my classic car’s engine.

So I went with the pre-programmed model, the 123/MINI-R-V.

Mmm, shiny. The handbook comes with a chart of the 14 different curves, and you select a curve using the rotary switch:

In my case curve E matched the existing distributor’s curve from 2000rpm and up, but had the correct advance at idle too. Perfect! It was installed and the engine started right up, a bit of tweaking to get the timing spot on, and that was it.

However… the 123ignition distributor cap is even less waterproof than the old Lucas 45D4, which is quite a remarkable feat. The Lucas distributor has an extra flange where the distributor cap meets the body, forming a reasonable seal. The 123 has a large, thirsty gap. Not a problem on a sensibly-designed car, but not great on a Mini where the distributor sits up against the grille.

I’ve designed and 3D printed a water deflector/seal that slips onto the 123 distributor body and fits closely to the distributor cap. The seal has an internal air gap and drain channels to let any water escape. Sealing could be further improved with some silicone grease between the seal and distributor cap, but I haven’t needed it yet.

I’ve published the design on Thingiverse here so anyone can print one of their own out of flexible TPU rubber filament.

Lowering the RPMs

The 3.44:1 final drive is great for acceleration, perhaps a little too good: full throttle is unusable in 1st gear, and you have to take care in 2nd in the wet. But the main issue is doing 4000rpm at 100kph. It’s not very relaxing. So I’m biting the bullet and rebuilding the gearbox with a 2.76:1 final drive, as fitted to the late ’90s Minis.

I’ve also got a Kent 246 “high torque” cam, but the existing MD266 is already quite torquey so I’m going to leave it in and see how it copes. I can always change the cam later. Right: remove engine, rebuild gearbox.

While the gearbox is apart I’ve also put new springs in the synchro hubs (not enough tension on the old springs so it was grinding into 3rd), smoothed out the selector rail detent notches (now wave shaped for smoother shifting), and shimmed the layshaft to spec by putting shims behind the small thrust washer.

As expected, acceleration is very much reduced. On the other hand I can get to 100kph in 2nd now, so 0-100 time is about the same. The MD266 cam seems to be just fine, with enough torque to pull well in any gear.
Here’s the road speed/rpm graph thanks to Guess-Works online Mini gearbox calculator (Original final drive is in green, new 2.7:1 is in white)

3rd gear is for overtaking and cruising around town, 4th gear feels like 5th in a modern car. Nice and (relatively) quiet for cruising. I call this a success.

Lucas, Prince of Cost Cutting.

Having owned many old and rare cars, and being quite familiar with the idea of desperately scrounging in junkyards to find one tiny but critical part, one of the nicest things about owning a Mini is the availability of almost every part, brand new, often from the original manufacturer.

Except sometimes the quality isn’t quite the same as it was in the 1960s. Take the light switch, for example. Last night we were ready to head off to Mini club, flipped the switch and… sproing! No lights, no clicky noise from switch. Abandon Mini, drive in the Terios (AKA “the car that always works” or “the car I’m not allowed to pull apart”)

It seems Lucas has decided to make the internal parts of their new switches from plastic. Soft, chewy plastic which is in no way up to the task of resisting the pull of two short but strong springs. Like so:

We have a new replacement on the shelf, but I’m not keen on fitting another switch which will crap out as soon as the first one. Luckily I have a few old, original 1960s Mk1 switches in a box somewhere. Look at all that high-quality (if extremely dirty) steel:

The steel slwitch levers fit into the new switch casing with no trouble at all.

So now I have a new switch with 1960s internal parts. It should last another 50 years.

New shoes! Or is it feet?

Rupert has new shoes! Or is it new feet?

Our old steel wheels were genuine Dunlop LP883 wheels as fitted to Coopers. They looked great, but they weren’t particularly round or straight. No matter how accurately balanced, there was always a bit of shimmy at 100kph. Straightening them was going to be expensive with no guarantee of success, and so we’ve given in and replaced them with Minisport LP883 Cooper wheel lookalikes in alloy. (Minisport part number SPDSR-011-W)

The product information on Minisport’s website is a bit sparse, so buying these felt risky. The price made it easier though: we landed them in New Zealand for less than $400. Even if they didn’t fit, we could have flogged them on TradeMe and made our money back.

But they do fit. And rather well too.

New wheels with hubcaps

New wheels without hubcaps

In case you’re thinking of buying these, here’s my review:

A lovely alloy LP883 lookalike with near identical fit and backspacing. Vent holes are teardrop shaped rather than round, but it’s only noticeable at certain angles. Colour is bright white (think refrigerator white) rather than Old English White. (Ours are painted to match the roof).

They fit over 7.5″ disc brakes with 5mm calliper clearance at the rim. Clip-on balancing weights *just* touched the bleed screw boss, which was easily relieved with an angle grinder. The LP883 Cooper hubcaps fit perfectly, though they sit about 8mm further out than on a steel wheel. It’s subtle.

The main issue we faced is that they’re thicker than steel wheels (obviously) so we needed longer wheel studs. The rears were easy, as there’s a large range of rear wheel studs available, but front studs for disc brake hubs only come in two lengths- and we already had the longest ones.

Edit: Brian thinks I should explain why this is an issue with these wheels, when people fit alloys to Minis all the time without issue. It’s the wheel nut seat. Most alloys use a conical seat nut with a 60 degree angle, but these ones have a spherical seat like the steel wheels they’re replacing. For authenticity.


For the same size wheel nut, a 60 degree taper gives more depth into the wheel and more thread engagement. So what’s the solution? Minisport’s suggestion was to use enclosed wheel nuts, which didn’t really make sense to me. It wouldn’t change how many threads were engaged, it would just make it harder to observe. The solution of last resort would be to machine 60 degree seats into the wheels, making them like most other alloy wheels, but that’s expensive and I’m cheap.

Rear wheel installed

In the end I tracked down some Polaris RZR wheel studs that were the correct size and length- but were only grade 5. (Polaris part #7517871, 3/8x24tpi, 1.73″ / 44mm long). Luckily(?) they’re a known weak spot, and there are a bunch of aftermarket wheel studs available which are grade 8 or higher. We’ve ordered a set of CV racing Xceldyne studs, part # CV4-1242.

Front wheel studs length comparison

Top right is the old 35mm stud (21A2064). We’re about 3 threads short of full engagement, which isn’t enough  (Rule of thumb: you want 1.5 times the bolt diameter engagement, which comes to about 14mm. These wheel nuts are- you guessed it- 14mm long). It’s also not enough to pass a safety test here- inspectors require full engagement with the nut, plus one or two threads. The other 3 studs are the Polaris ones, and we’ve got full engagement plus 2 threads so they’re about perfect.

More clean things… and a flywheel.

Here we go, more things through the molasses bath. The flywheel, pressure plate, and sandwich plate:





So clean you can even see the timing marks:


And yes, that’s a Morris 1300 flywheel, the heaviest ever fitted to an A-series, even heavier than a standard Verto unit. A 1275 engine isn’t the best balanced machine, and a heavy flywheel does a lot to smooth it out- this should give me the quiet idle I’m looking for. The car will have slower acceleration in lower gears, but that might be good- a bit like traction control. At the moment it’s far too easy to overcook it and just spin the wheels.

Molasses for de-rusting

Molasses is rich in chelates, chemical compounds which latch onto iron oxides and pull them into solution. Soak a rusty thing in molasses, the theory goes, and all the rust will go away. Eventually.

Molasses is also really cheap if you buy it from a farm supplies store. 12kg for about NZ$20. Mix it 1:3 with water, and soak away, stirring every couple of days to encourage the chelated rust to move away from the surface.

It works! It’s completely gross, but it works!


That’s what a tank of molasses looks like after sitting for 2 weeks. Not pleasant. It might have been less disgusting if I had left the lid off. The molasses won’t remove paint or oil, so I had to wash the block before soaking it. The engine paint was pretty crappy and came loose after a week’s soak, so a wire brush was enough to remove it.

Once the rusty thing has soaked for a couple of weeks, it comes out coated with black sludge, which hoses off easily to reveal lovely clean metal underneath.

Before and after shots:











I’m pretty happy. The results are better than the $100 hot tank clean we had done to our last engine, it cost $20, and the molasses bath is still perfectly useful for other things (I have the flywheel and pressure plate in there now).

Bearing race extraction by welding

Work continues on the new/spare engine. I finally found the courage to try that welding trick to remove a bearing race from a blind hole. Bugger me, it works.




I shouldn’t have been so surprised. I’ve warped enough steel with weld to know that weld shrinks as it cools. Welding so close to a large, complicated, precision aluminium casting is a bit fraught though.